Reference is made to U.S. Pat. No. 3,986,897 entitled "Aluminum Treatment to Prevent Hillocking" granted Oct. 19, 1976 to L. D. McMillan et al. The McMillan et al patent discloses a method of surface treating aluminum, particularly aluminum metallization for semiconductors, which includes subjecting the aluminum surface to be treated with fuming nitric acid for one to ten minutes at room temperature. Following cleaning, the surface is subjected to boiling water for 5 to 15 minutes. The foregoing treatment appears to form a boehmite (AlO(OH) layer on the surface of the aluminum, thereby substantially eliminating hillocking.
Reference is made to U.S. Pat. No. 4,068,018 entitled "Process for Preparing a Mask for Use In Manufacturing A Semiconductor Device" granted Jan. 10, 1978 to T. Hashimoto et al. The Hashimoto et al patent discloses a process for preparing a mask, such as a photo-mask, used in a selective etching process in the manufacture of a semiconductor device or a protective mask for use in a process for selectively providing a porous layer of silicon or for anodic oxidation of a metal layer, in which ions accelerated at a predetermined voltage are implanted into a photo-resist film to a predetermined dose level.
Reference is made to U.S. Pat. No. 4,089,709 entitled "Method for Passivating Aluminum Layers on Semiconductive Devices" granted May 16, 1978 to J. M. Harris. The Harris patent discloses an aluminum layer such as an intraconnect on an integrated circuit semiconductive device is passivated by oxidizing the aluminum layer to form a thin layer of amorphous alumina thereon. The alumina layer is coated with a surface active agent to form a hydrophobic surface on the aluminum oxide to inhibit the creation and growth of ALOOH on the oxide layer. The hydrophobic surface is coated with a conventional passivating material such as silicon dioxide, epoxy or the like.
Reference is made to U.S. Pat. No. 4,118,250 entitled "Process For Producing Integrated Circuit Devices by Ion Implantation" granted Oct. 3, 1978 to C. T. Horng et al. The Horng et al patent discloses a process of producing a bipolar transistor where all the regions of the device except the emitter region are formed by ion implantation through an inorganic dielectric layer of uniform thickness. Subsequently, all the contact openings to the emitter, base and collector are formed and the emitter is implanted through the emitter contact opening. This unique combination of process steps permits the use of a surface insulating dielectric layer of uniform thickness, wherein all capacitances are uniform and controllable while still permitting direct implantation of the emitter, which, because of its shallow depth is difficult to implant through an oxide.
Reference is made to the anodization process disclosed and schematically illustrated in FIG. 1 of the publication entitled "Identification of Crystal Defects Causing Diffusion Pipes" by D. K. Seto, F. Barson and B. F. Duncan in Semiconductor Silicon 1973, H. R. Huff and R. R. Burgess, Ed., The Electrochemical Society Softbound Symposium Series, 1973, pp. 651-657.
Reference is made to the publication "Anodic Oxide Films on Aluminum" by J. W. Diggle, et al. Chemical Reviews Vol. 69, 1969 pages 365-405.
In the prior art so called "double-diffused" bipolar transistor, a base region is formed by a selective diffusion into a collector region and an emitter extending only partially in the base region is formed by a second diffusion. The emitter diffusion in most applications is done at a temperature considerably higher than that for the base diffusion. This high temperature diffusion cycle redistributes the base doping profile previously formed by the base diffusion.
For a vertical bipolar transistor the part of the base region situated directly below the emitter is the active base region. The impurity doping profile and the width of the active base determines the emitter injection efficiency, current gain and device speed. The base region that surrounds the emitter is the inactive base. The metal to base contact is formed over the inactive base region. The doping in the inactive base region determines the emitter-base breakdown characteristics and the external base resistance.
For good high frequency response it is important that the base width is narrow and the active base region is lightly doped. It is also important that the inactive base is heavily doped to lower the base series resistance and metal-base contact resistance.
In the conventional double-diffused bipolar transistor, as the device depth is reduced to improve the device speed performance, control of the integrated base doping in the active base region while maintaining a low sheet resistance in the external base region becomes increasingly difficult. In order to obtain an improved transistor structure, the impurity doping profiles in the active base and the inactive base have to be controlled by separate, independently processes. To achieve a controllable narrow base width it is desirable that the active base be formed "in place". To accomplish the above mentioned goals it is necessary that ion-implantation instead of the conventional thermal diffusion process be used for doping the inactive and active base.
Ion-implantation provides a means for precisely controlling the total amount of impurity transferred to the wafer. The impurity depth distribution is accurately controlled by implant energy. Unlike the conventional thermal diffusion process, ion implantation is not a high temperature process. Implantation into the silicon can be made through the surface passivation layer. Thus, by using photoresist or metal maskings, different impurity introductions into the semiconductor can be achieved without resort to various high temperature diffusions. A final thermal heat-treating is sufficient to anneal out the radiation damage caused by implantations and obtain the desired device junction depth. Consequently, integrated circuit devices can be made shallower, with greater precision on the impurity distribution using ion-implantation technology.